| Abstract
| - Aims. We use Hubble Space Telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Ly α) halos, Ly α morphology, and the star-forming characteristics of galaxies. We study how the morphology of Ly α emission is related to other Ly α observables. Furthermore, we study the interdependencies of Ly α morphological quantities. Methods. We studied the spatial extent of Ly α using surface brightness profiles in the following two ways (i) using circular apertures and (ii) within faint Ly α isophotes. We also measured the average intensity and the size of the regions with a high star formation rate density. The morphology of the galaxies was quantified by computing centroid position, axis ratio, and position angle in the Ly α, ultraviolet continuum, and I band maps. Results. We found that galaxies with more extended star-forming regions possess larger Ly α halos. Furthermore, galaxies with more elongated Ly α morphology are also more extended in Ly α. Our data suggest that Ly α bright galaxies appear rounder in their Ly α morphology, and there is less of a contribution from their Ly α halo to their overall luminosity. We compared our results with studies at high redshift and found that whilst the Ly α extent in the inner regions of the galaxies in our sample are similar to the high- z Ly α emitters (LAEs), Ly α halos are more extended in high- z LAEs. Conclusions. Our analysis suggests that the Ly α morphology affects the measurement of other observable quantities concerning Ly α emission, and some of the conclusions drawn from high redshift LAEs might be biased towards galaxies with specific Ly α shapes. In particular, faint Ly α emitters have larger Ly α scale lengths and halo fractions. This implies that faint Ly α emitters are harder to detect at high redshift than previously believed.
|
